This invention is directed to a method of providing insulating material on a semiconductor substrate, and more particularly, to a method of providing an insulating layer of titanium dioxide in a form known as rutile upon a silicon semiconductor substrate.
Since the invention of metal insulator semiconductor (MIS) field effect transistors, the insulator that has been used almost exclusively has been silicon dioxide. There are several reasons for this, not the least of which is the compatibility with standard semiconductor fabrication technology. Oxidation of silicon to form silicon dioxide is one of the simplest, most accurate and most frequently used procedures in the semiconductor fabrication process. The use of silicon dioxide has worked well for many years, and it continues to be the most used insulator for MIS devices. As integrated circuits have become more and more dense, the individual MOS devices on them have become smaller and smaller. As the device size is reduced, the oxide thickness must be reduced accordingly to achieve corresponding size reductions. However, as this oxide thickness is reduced, the oxide becomes more susceptible to process-induced defects, such as pinholes, which made it difficult to obtain satisfactory device yields. Consequently, there has been an effort to use insulators with higher dielectric constants so that the insulator thickness can be maintained thick enough to avoid the thin oxide problem and yet not significantly affect device threshold voltages. Devices have been built using a combination of silicon dioxide and silicon nitride, but the dielectric constant of nitride is only about twice as high as silicon dioxide and the improvement has generally not been worth the extra processing effort. Titanium dioxide is an insulator which can exist in three crystalline forms: anatase, brookite and rutile. Rutile is the more thermodynamically stable of the three forms and in polycrystalline form has a dielectric constant of approximately 125, which is 32 times larger than that of silicon dioxide. Some work has previously been done using rutile as an optical coating. This work is described in a paper by G. Hass, Vacuum, Vol. II, No. 4, October, 1952, pp. 331-345. In forming rutile as an optical coating, pure titanium metal was evaporated upon glass and then oxidized.